Phased array fed lens antenna

ABSTRACT

A phased array antenna functions as a source of electromagnetic energy directed toward a non-planar lens positioned in the near field of the phased array antenna. The non-planar lens includes a plurality of modules comprised of collector elements, phase shifter elements and radiator elements. Electromagnetic energy radiated from the feed antenna to the plurality of collector elements in the non-planar lens is coupled from the collector elements through the phase shifter elements to the radiating elements. Each phase shifter has a fixed delay which acts upon the electromagnetic energy transmitting through the phase shifter so that the electromagnetic energy radiated by the associated radiating element combines with the radiated energy from the other radiating elements to produce a beam having a modified scan angle relative to the scan angle of the emitted beam from the phased array antenna.

[ Aug. 28, 1973 1 PHASED ARRAY FED LENS ANTENNA [75] Inventors: John J.Stangel, Mahopac; Pasquale A. Valentino, Brooklyn, both of NY.

[73] Assignee: Sperry Rand Corporation, New

York, NY.

[22] Filed: Dec. 20, 1971 [21] Appl. No.: 209,863

Primary Examiner-Benjamin A. Borchelt Assistant Examiner-S. C. BuczinskiAttorney-l-Ioward P. Terry 57] ABSTRACT A phased array antenna functionsas a source of electromagnetic energy directed toward a non-planar lenspositioned in the near field of the phased array antenna. The non-planarlens includes a plurality of modules comprised of collector elements,phase shifter elements and radiator elements. Electromagnetic energyradiated from the feed antenna to the plurality of collector elements inthe non-planar lens is coupled from the collector elements through thephase shifter elements to the radiating elements. Each phase shifter hasa fixed delay which acts upon the electromagnetic energytransmittingthrough the phase shifter so that the electromagnetic energyradiated by the associated radiating element combines with the radiatedenergy from the other radiating elements to produce a beam having amodified scan angle relative to the scan angle of the emitted beam fromthe phased array antenna,

20 Claims, 23 Drawing Figures PATENTEDAUB28 ms 3; 75513 1 5 sum n2ur13FEED ARRAY FIG.3Q.

FEED ARRAY FiG.3b.

rmminmsze ms SHEEI 03 0F 13 SCAN ANGLE FROM ZENITH 33 2:6 25:52 mZbIwmPATENIEDMIGZB ma 3,755,815

sum as 0F 13 DIPOLE RADIATOR ELEMENTS LENS STRUCTURE FLEXIBLE CABLESDIPOLE COLLECTOR ELEMENTS FIG.7.

RADIATOR LENS STRUCTURE MATCHING STRUCTURES WAVEGUIDE ELEMENTSICOLLECTOR S I DE FIG.8.

- PAIENTEMucza ma 3.755815 sum ur 13 \l l I SCAN ANGLE 3O ii [Iv W SCANANGLE Pmmmmzams 3.755815 SHEET HF 13 n/ \M 15 10 A A SCAN ANGLE SCANANGLE mememucza ms MEI 11 01 13 SCAN ANGLE 0 FiG.l0|.

SCAN ANGLE PATENTEMucze ma 3.7 55815 saw 13 or 13 PHASED ARRAY FED LENSANTENNA BACKGROUND OF THE INVENTION 1. Field of the Invention Thesubject invention pertains to the art of antennas and specifically to acombination antenna which includes a phased array antenna and a lensantenna.

2. Description of the Prior Art In many of the early antennas that weredeveloped for radars before World War II array antennas were used atrelatively low frequencies, i.e., VHF or low UHF. However, with theadvent of microwave radar and the application of optical techniques tomicrowave frequencies, interest in array antennas declined whileinterest centered on reflector antennas and lenses. These types ofantennas were easier to design, simpler to manufacture and provedsufficiently reliable in operation.

In the last decade interest has been refocussed on array antennas,particularly phased array antennas because the speed of potentialtargets has greatly increased and it has become imperative to detect thetarget as soon as possible thereby requiring an increase in range.Further, the ability to simultaneously track a plurality of targetsvirtually eliminates the use of an antenna which requires the physicalmovement of a large mass. Therefore, phased array antennas which may beelectronically steered at very high rates and which may simultaneouslytrack a plurality of targets by producing time-shared radar beams arerequired.

In the prior art, phased array antennas have usually been designed inone of four geometrical configurations; linear, planar, cylindrical orspherical. The construction and design of cylindrical and sphericalphased arrays is more complex and more expensive than the planar arrays.Further, curved phased arrays are less efficient than a planar arraybecause they do not utilize all the radiating elements at specificangles of scan due to the curvature of the array.

The most common configuration used is the planar array which has amaximum gain 6(0) of a directive beam in a direction as measured fromthe outward normal of the array that is bounded by:

0(0) (411-03) A cos 0 where A is the area of the antenna and X is theoperating wavelength. The maximum value of the scan angle 0 is limitedto less than 90 in principle and less than 70 in practice because of thedifficulty in economically realizing efficient operation over extendedscan ranges. Forhemispheric coverage the use of a planar array has beensummarized in an article entitled Electronic Scanning Radar Systems" byPeter J. Kahrilas, which appeared in the Proceedings of the IEEE,November 1968, In the case where hemispherical coverage is required thechoice exists among the following: (1) four arrays, each coveringapproximately one-quarter of the hemisphere, or (2) three arrays, eachcovering approximately one-third of the hemisphere or (3) one array,mechanically rotating in azimuth and electronically scanning a pencilbeam in elevation from 0 to 90.

The single array can only be used for hemispherical coverage if it canmeet the data rate and performance requirements, and if the targetdynamics and target density are low enough to employ track-while-scaninstead of continuous interpolative-null tracking.

Lens antennas are also well known in the radar antenna art. They havebeen used primarily for transforming a spherical wavefront produced byrays emerging from a smaller feed antenna into a flat or uniphasewavefront at the aperture of the lens. Metal-lens antennas which utilizethe optical properties of radio waves have been the subject of anarticle by Winston E. Kock which appeared in the Proceedings of the IREand Waves and Electrons, November 1946, pages 828-836.

Furthermore, radomes which are primarily used to protect antennas fromsevere weather conditions such as high winds, icing and extremetemperatures have been used in combination with antennas in the priorart to modify the polarization of radiated beams and to alter the phaseconfiguration thereby compensating for radome phase distortion. In theseapplications the radomes may be considered to be functioning as lenses.

The subject invention discloses the use of a single planar phased arrayantenna in combination with a non-planar antenna lens which modifies thescan characteristics of the planar array to enable increased angularscan off broadside. One embodiment provides full hemispheric coverageusing a single planar phased array antenna and a single passive lens.

SUMMARY OF THE INVENTION terns having characteristics, i.e., beamwidthand gain,-

that vary in accordance with the scan angle to conform to a givenoperational requirement. The lens'may be a constrained type whichincludes a plurality of modules comprised of collector elements, phaseshifter elements and radiator elements or may be a dielectric type.Electromagnetic energy radiated from the planar array portion of theantenna (referred to as the feed array) is directed to the lens andcoupled therethrough to the radiating surface. The phasing of the feedarray is such that when the electromagnetic energy is transmittedthrough the lens, the total electromagnetic energy radiated by theradiating surface of the lens combines to produce a collimated beam at aspecific scan angle 0'. By changing the phasing of the feed arraydifferent collimated beams at different scan angles are generated. Thelens imparts a phase delay to the incident electromagnetic energy whosevalue depends on the portion of the lens upon which the energy isincident. This causes the pattern characteristics of the collimatedbeams formed by the antenna to conform to the desired operationalrequirement.

When the phase gradients imposed by the lens are such thatelectromagnetic energy from the center of the feed array incident on thelens is refracted toward the broadside direction, the effect of the lensis to reduce the scan range of the planar phased array. However, toproduce a collimated beam in the broadside direction, the planar arraymust be phased to form a diverging wave which has the effect ofincreasing the gain of the radiated beams in the vicinity of broadsideto a value which is greater than that obtainable with a planar array ofcomparable size and number of elements in the feed array.

Further, when the phase gradients imposed by the lens are such thatelectromagnetic energy from the center of the feed array incident on thelens is refracted away from the broadside direction, the effect of thelens is to increase the scan range of the planar array. Then, to producea collimated beam in the broadside direction, the planar array must bephased to form a converging wave which has the effect of reducing thegain of the radiated beams in the vicinity of broadside.

In the most general case, however, the phase gradients imposed by thelens are such that rays from the center of the feed array are refractedby varying amounts either toward broadside or away from broadsidedepending on which region of the lens they are incident. Then, toproduce collimated beams, the feed array must be phased to form apredominately divergent wave for some directions of scan or apredominately convergent wave for other directions, resulting incorresponding increases or decreases of gain in those scan directionsrespectively.

Proper determination of the variation of phase delay in the lens causesthe gain of the collimated beams to vary with scan angle in accordancewith a prescribed operational requirement. Moreover, a directconsequence of achieving this high degree of conformity to theoperational requirement is to reduce the size and number of elements inthe feed array to an extent not possible with prior art antenna systems.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representationof an antenna including a feed horn, a feed array and a lensillustrating the refractive action of the lens with respect to the feedarray;

FIG. 2a is a typical ray diagram ofa convergent beam from a phased arraydirected at a lens having a scan amplification factor greater than 1which produces a beam parallel to broadside;

FIG. 2b is a typical ray diagram of a phased array convergent beamdirected at a lens having a scan amplification factor greater than Iwhich produces a beam at an angle of approximately 60 with respect tobroadside;

FIG. 3a is a typical ray diagram of a divergent beam from a phased arraydirected at a lens having a scan amplification factor less than 1 whichproduces a beam parallel to broadside;

FIG. 3b is a typical ray diagram of a divergent beam from a phased arraydirected at a lens having a scan amplification factor less than 1 whichproduces a beam at an angle of approximately with respect to broadside;

FIG. 4 is a graph of the relative aperture gain versus scan angle of acircular arc cylindrical lens;

FIG. 5 is a graph of gain versus scan angle from zenith for athree-dimensional wide angle scanning array;

FIG. 6 is a graph of antenna diffraction patterns of a circularcylindrical lens having a scan amplification factor of 1.5 for beampointing directions of 0, 30, 60 and 90 with respect to broadside;

FIG. 7 is a schematic diagram ofa lens in a combined phased arrayantenna and lens in which the lens includes dipoles;

FIG. 8 is a schematic diagram ofa lens in a combined phased array andlens in which the lens includes circular waveguide elements;

FIG. 9 is a diagram of a hyperbolic nose cone dielectric lens and feedarray;

FIGS. 10a-j are graphs of radiation patterns computed for a hyperbolicnose cone lens having a 5.5 cone half-angle;

FIG. 10a shows the pattern for 0 scan angle with 4.88 dB edge taper feedarray illumination;

FIG. 10b shows the pattern for 0 scan angle from a uniformly illuminatedfeed array;

FIG. shows the pattern for 30 scan angle from 4.88 dB edge taper feedarray illumination;

FIG. 10d shows the pattern for 30 scan angle from a uniformlyilluminated feed array;

FIG. 102 shows the pattern for 60 scan angle from 4.88 dB edge taperfeed array illumination;

FIG. 10fshows the pattern for 60 scan angle from a uniformly illuminatedfeed array;

FIG. 10g shows the pattern for 90 scan angle from 4.88 dB edge taperfeed array illumination;

FIG. 10h shows the pattern for 90 scan angle from a uniformlyilluminated feed array;

FIG. l0i shows the pattern for scan angle from 4.88 dB edge taper feedarray illumination;-

FIG. l0j shows the pattern for 120 scan angle from a uniformlyilluminated feed array;

FIG. 11 is a cross-section of a spherical lens and a feed arrayradiating a convergent beam in a first direction and a divergent beam ina second direction;

FIG. 12 is a schematic representation of an antenna comprising a feedhorn, a feed array and a lens in which the lens includes variable phaseshifter elements.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a typicalembodiment of a phased array lens antenna 10 which includes a lens 11which is substantially hemispherical in shape and has a plurality ofcollector elements 12 coupled through phase delays 13 to correspondingradiator elements 14. Positioned in the near field of the lens 11 is afeed array 15 which includes collector elements 16 coupled through phaseshifter elements 17 to radiator elements 20. A feed horn 21 illuminatesthe collector elements 16 of the feed array 15 with electromagneticenergy received at the input to the feed horn 21. The feed array 15 isof sufficient size and proximity to the lens 11 to illuminate it with asearch light" effect, i.e., the lens 11 is sufficiently in the nearfield of the feed array 15 to prevent a highly diffracted radiated beampattern from forming.

While the phase delays 13 in the lens 11 may be variable, in order tosimplify the explanation of the invention, they will be considered to befixed phase delays and the phase shifters 17 in the feed array 15 areelectronically controlled phase shifters which vary the direction of theradiated beam from the feed array toward the inner surface of the lens11. The maximum aperture gain of the antenna comprising the lens andfeed array in any given direction is given by G (Mr/It) A (0) where A(0) is the area of the lens 11 projected in the given direction.

Assuming the delays 13 are fixed, it is necessary to determine thevariations in the values of thefixed phase delays 13. Consider as shownin FIG. 1, a ray 22 emanating from the midpoint of the feed array 15 atan angle 0 with respect to the normal, N, of the plane, XX, of the feedarray 15. The refractive action of the lens 11 is considered asoccurring at a fictitious surface 23 as shown in FIG. 1 and locatedmidway between the inner and outer surfaces of the lens 11. The ray 22is incident on the surface 23 at a point 24 and is refracted by the lensto an angle 0'. For the given geometry, this refraction uniquely definesa gradient of phase, tangential to the surface 23, at the point 24. Byvarying 0 so that the ray 22 is incident upon the lens 11 at positionscorresponding to each of the plurality of collector ele ments 12, thephase gradient at every point corresponding to the fixed delays 13 onthe surface 23 may be defined and thereby the relative values of theadjacent fixed delays 13 can also be defined. The ratio of 0' to 6 iscalled the scan amplification factor, K.

For a spherical lens 11 of radius R and a constant scan amplificationfactor K, the values of the fixed phase delays 13 in the lens 11 may bedetermined as functions of 0 as given in terms of wavelengths by: delay(R/K l) [1 cos (0' 0)].

When the values of the fixed delays 13 in the lens 11 have beenestablished in the foregoing manner, the phasing of the feed array toobtain a well collimated beam scanned in a direction 6 must bedetermined. This is done by considering a plane wave incident on theouter surface of the lens 11 from the direction 0 and computing thefield as it penetrates the lens 11 and irradiates the planar feed array15. The required phasing of the feed array is then that of the complexconjugate of this field.

In many practical applications of this invention, the computation fordetermining the required phasing of the feed array 15 may be simply andvalidly performed by geometrical optic techniques. The cross-sectionspherical lens 11 having a value of K greater than 1 is shown in FIGS.2a and 2b in combination with a feed array 15 that provides a convergingbeam as indicated by the plurality of rays 22a-e.

In FIG. 2a, the rays are directed toward the inner surface of the lens11 and exit from the outer surface of the lens 22 as a directive beam.In FIG. 2b, the beam, as represented by the plurality of rays Ila-e, isdirected toward the inner surface of the lens 11 to the right of thenormal, N, and exits from the outer surface of the lens 11 as adirective beam. It will be noted that the angles 0 -6,, have beenincreased with respect to the normal, N, to angles 0,,-6 which are allequal forming the directive beam which exits from the lens 11. Therefraction is different for each ray 22a-e because the angles (fl -0 arenot equal but the angles (if-0 are equal.

The image of the aperture of the feed array 15 as projected through thelens 11 for scan directions near the normal, N, is less than that of thefeed array 15 without the lens 11. Therefore, while an antenna comprisedof a feed array 15 and a lens 1] having a scan amplification factor, K,greater than 1, will increase the scan range of the planar feed array 15there is a reduction of gain for beams near broadside.

A spherical lens 11 having values of K less than I is shown in FIGS. 30and 3b in combination with a feed array 15 that provides a divergingbeam as indicated by the plurality of rays 22f-j. In FIG. 3a, the raysare directed toward the inner surface of the lens 11 and exit from theouter surface of the lens 11 as a directive beam. In FIG. 3b, the beam,as represented by the plurality of rays 22f-j, is directed toward theinner surface of the lens 11 subtantially to the right of the normal, N,and exits from the outer surface of the lens as a directive beam. Itwill be noted that the angles 0,-0, have been decreased with respect tothe normal, N, to angles Of-B, which are all equal and form thedirective beam which exits from the lens 11. While this has the effectof reducing the range of scan of the antenna, it provides an increase inthe gain of the beams in the vicinity of broadside beyond that whichcould be achieved with a planar feed array comparable in size and numberof elements to that in the feed array 15.

FIG. 4 is a graph of scan angle versus relative aperture gain in dB fora linear feed array 15 and a circular arc cylindrical lens 11. The ratioa/p defines the ratio of the feed array size to the radius of the lensin which a is the length of the feed array and p is the radius of thelens. The K 1 plot represents the case where the lens does not impart aphase variation to the incident energy and hence represents the feedarray alone for all values of a/p. The two plots of antennas comprisedof a feed array and lens in which the scan amplification factor, K 0.5shows an increase in gain with an attendant reduction in the angle ofscan. The two plots of an antenna having a scan amplification factor, K1.5 and the two plots of an antenna having scan amplification factor, K=2.0 show a reduction in the relative aperture gain with an attendantincrease in the range of scan.

FIG. 5 is a graph of scan angle versus relative gain in dB for a planarfeed array 15 and spherical lenses 11 having scan amplification factorsK 1.0, 1.5, 1.75 and 2.0. These plots show the envelope of the peak gainof the antenna as the beam is scanned from the normal, N, relative tothe broadside gain of a planar array having a size comparable to thefeed array 15.

The plots in FIGS. 4 and 5 graphically illustrate that for applicationsrequiring a scan range of less than 45 from the normal, the effect ofthe invention is to reduce the size of the array 15 and therefore reducethe number of phase shifters l7 needed to realize a given gain. Further,for applications requiring an extremely wide scan coverage, i.e.,greater than with respect to the normal, the effect of the invention isto provide a mechanism for efficiently generating the desired angularcoverage with a single planar array 15.

FIG. 6 shows the computed diffraction patterns of an antenna employing acircular cylindrical lens having a scan amplification factor, K 1.5 withthe collimated beam directed at 0, 30, 60, and and the sidelobesmaintained at a maximum of -28 dB relative to the respective beam peak.

A more general approach to the use of the scan amplification factor, K,for selecting the values of the fixed delays 13 in the lens 11 is basedon the envelope of the peak gain of the scanned beams which is theaverage power patternof the elements in the feed array 15, as measuredin the far field in the presence of the lens 11. The average powerpattern of the element in the feed array 15 would be the gain versusscan variation of the feed array alone. The lens 11 acts to alter theelement pattern of the feed array 15 and hence the gain-versusscanvariation of the antenna 10. A method for tailoring the element patternof the central element of the feed array 15 is based on a technique wellknown in the art of designing shaped reflectors. For a completediscussion of this technique, reference is made to Microwave AntennaTheory and Design, Samuel Silver, McGraw-Hill, New York, 1949, pages494-500. This technique defines the relationship between the angles 6and 0 using geometrical optics so as to provide the proper fiow ofenergy required to synthesize the desired element pattern shape. In asymmetrical system, the 6-0' relationship is expressed by the integralequation:

I G() sin ()dQ-f G (0) ma 0 0 9 Sln where 6 (0) is the element gainpattern of the feed array without the lens and C(19) is the desiredelement gain pattern of the feed array 15 with the lens 11 or thedesired normalized gain-versus-scan variation of the antenna 10. Whenthe relationship between 6 and 0 is so defined, the values of the fixeddelays 13 are determined in a manner identical to that described in thetechnique employing the scan amplification factor.

This approach for selecting the values of the phase delays 13 in thelens 11 enables the design of lens-array systems which satisfy moresophisticated requirements than possible using the constant scanamplification approach. For instance, an application may dictate that aconstant signal be maintained from a ground based system at a specificaltitude over a given range. This requires a broad beam with low gaindirectly overhead and narrow beam with high gain at wide scan angles.FIG. 11 shows a phased array fed spherical lens applicable to thisrequirement. The phase delays in the lens are determined using thetechnique described in the above paragraph. Thus, for a scan directiondirectly overhead the feed array 15 is phased to provide a highlyconvergent beam of electromagnetic energy. As illustrated in FIG. 11,this results in only a small section of the lens being illuminatedresulting in a broad beam with low directive gain. For the scandirection requiring the narrowest beam with the highest gain, the feedarray 15 is phased to form a divergent beam of electromagnetic energy.As illustrated in FIG. 11, this results in a large portion of the lensbeing illuminated resulting in a narrow beam with a high directive gain.For scan angles in between these two, the lens phase delays necessitatethe phasing of the feed array be such as to illuminate a portion of thelens of sufficient size to satisfy the beamwidth and gain requirementsin the specific direction of scan.

In operation, electromagnetic energy from a feed horn 21 as shown inFIG. 1 is radiatedtoward the collector elements in the feed array 15 andcoupled through electronically controlled phase shifters 17 to theradiator elements 20 on the feed array. The electronically controlledphase shifter elements 17 determine the direction of the radiated energyfrom the radiating elements 20 toward the inner surface of the lens 11.The phasing of the radiated energy from the feed array 15 determineswhich of the plurality of collector elements 12 on the lens 11 receivethe radiated energy from the feed array 15. These collector elements 12couple the received energy through the fixed phase delays 13 to theradiator elements 14 on the lens 11 and provide a directive beam ofelectromagnetic energy from the antenna 10. The characteristics of theradiated beam from the antenna 10 are determined by the lens phaseshift, the length of the feed array 15 and the configuration of the lens11.

The lens 11 may be comprised of a variety of elements in accordance withtechniques that are well known in the lens and antenna arts. As shown inFIG. 7, one such embodiment includes dipole collector elements 30coupled through flexible cables 31 which function as fixed phase delaysmounted within the lens structure 11 and coupled to dipole radiatorelements 32. The length L of the flexible cable is varied from elementto element so as to provide the proper relative phase variation betweenthe transmission paths in the lens 11. An alternate configuration forthe lens 11 is shown in FIG. 8 wherein the collector elements 33 and theradiator elements 35 are open ended circular waveguides with appropriatematching structures 34 coupled therebetween. These elements aredielectrically loaded to provide a size sufficiently small forarrangement in a lattice capable of being matched over a wide range ofincident angles. The matching structure 34 is a circular waveguidesection loaded with two different dielectric materials of lengths L andL The sum of the physical lengths L and L is a constant for alltransmission paths within the lens 11 while the ratio of lengths L to Ldetermines the relative phase delay for a given element.

Although the element in the lens 11 may be arranged in a variety oflattice configurations, the inter-element spacing should be no greaterthan that dictated by the grating lobe condition:

Amin/l+sina where A is the minimum operating wavelength of the antennaand a is the maximum angle of incidence on the inner surface of the lens11 or transmission from the outer surface of the lens 11.

The subject invention may also be employed in an airborne system inwhich the lens 51 is a dielectric lens formed in a streamlineconfiguration to conform to the nose profile of a high speed aircraft asshown in FIG. 9. In one embodiment of the invention, a hyperbolic nosecone lens is fabricated of titanium dioxide and the geometry of the lensprovides a wide range of scan in excess of il20 with respect to the apexof the lens at a transmission frequency of 16 GI-Iz. Since the nose coneis a lens ofa homogeneous medium and not a constrained lens, i.e., alens with a plurality of transmission paths as provided by thecollectors, fixed phase delays and radiator elements of the lenses 11,the phase delay in the dielectric lens 51 is realized by means of achange in the refractive index of the lens material or by varying thethickness of the lens material between the base and the apex of the nosecone. The hyperbolic nose cone dielectric lens 51 shown in FIG. 9 has anasymptotic 5.5 cone half-angle, a scan amplification factor K 1.7 and afeed array length of 40 A.

FIG. 10a shows a radiation pattern for this lens at a scan angle of 0and a 4.88 dB edge taper feed array illumination and FIG. 10b shows theradiation pattern for the same lens at 0 scan angle with a uniformlyilluminated feed array. Similar results were obtained for the computedradiation patterns for the same nose cone under the same operatingconditions at 30 as shown in FIGS. 10c and 10d; at 60 as shown in FIGS.10e and 10fand at as shown in FIGS. 10g and 10h.

Although the computed radiation patterns for the hyperbolic nose conefor of scan angle showed a decrease in the directivity of the radiatedbeam due to increased width in the main lobe, it still provided sharpdiscrimination with respect to the sidelobes.

The lenses and arrays as disclosed are shown in one plane; however, itwill be readily appreciated that the spherical and hemispherical lenseswith scan amplification factors greater than 1 provide hemisphericalcovcrage, i.e., angles of scan greater than i90 from the broadsidedirection for all azimuth scan angles in the same embodiment. Therefore,rather than requiring three or four arrays to provide hemisphericcoverage, the subject invention requires a single planar feed array incombination with a lens having an effective scan amplification factorgreater than 1. In addition, it does not require mechanical rotation ofthe elements and thereby provides scanning at a maximum rate.

it will also be appreciated by those skilled in the art that thephysical structure required to implement the invention described hereinmay be fabricated of lightweight material and components known in theart which may be quickly assembled and disassembled for portability.

While the above embodiments employ feed arrays which incorporateelectronic phase controls only, the disclosed invention is equallysuitable to more sophisticated planar feed array configurations such asthose which incorporate devices for electronically controlling theamplitude and the polarization of the feed array excitation to enhancethe performance of the systern.

Further as mentioned previously, to simplify the explanation of theinvention, a passive lens has been cited in the foregoing embodiments.The lens however may be constructed in such a manner as to permitvariation of the phase gradient in the lens by either electronic ormanual means. This allows the scanning properties of the antenna to bealtered on a time scale consistent with the time required to effect thelens phase gradient variation. Used in conjunction with a multi-functionradar, for example, such a design facilitates optimization of each ofthe operating modes of the radar system. FIG. 12 shows a typicalembodiment of a phased array lens antenna substantially similar to thatshown in FIG. 1 except that the phase delays 13 of FIG. 1 are replacedby variable phase shifter elements 13'. Moreover, when electronic phaseshifters 13' are used to produce the phase delay in the lens 11, thevariation of gain with scan angle can be designed such as to approachthe maximum aperture gain of the antenna as previously defined. Then,the gain, averaged over all scan angles, will generally exceed thatrealizable by the equivalent antenna using passive phase delay in thelens 11.

While the invention has been described in its preferred embodiments, itis to be understood that the words which have been used are words ofdescription rather than limitation and that changes may be made withinthe purview of the appended claims without departing from the true scopeand spirit of the invention in its broader aspects.

We claim:

1. An electronic scanning antenna system comprising a source ofelectromagnetic energy,

array means including elements, said array means being coupled to saidsource of electromagnetic energy for producing a first beam ofelectromagnetic energy having a non-planar phase and controllable focalproperties, and

lens means responsive to said first beam of electromagnetic energyhaving a non-planar phase and controllable focal properties whichimplement a phase gradient for producing a directive second beam ofelectromagnetic energy having a plane wavefront, a variable range ofscan and an attendant variable gain.

2. An electronic scanning antenna system as described in claim 1 inwhich said source of electromagnetic energy includes a radiating feedhorn.

3. An electronic scanning antenna system as described in claim 1 inwhich said array means coupled to said source of electromagnetic energyincludes means for producing a converging first beam of electromagneticenergy having a pre-determined non-planar phase, said array means beingcapable of producing a first beam of electromagnetic energy at aspecific gain over a limited range of scan.

4. An electronic scanning antenna system as described in claim 3 inwhich said lens means includes means for varying said phase gradientwhereby said second beam of electromagnetic energy has an increasedrange of scan over said limited range of scan with an attendant minimumreduction of gain from said specific gain.

5. An electronic scanning antenna system as described in claim 3 inwhich said lens means has a fixed phase gradient in all directions fortransmitting a directive second beam of electromagnetic energy having aplane wavefront and an increased range of scan over said limited rangeof scan with an attendant minimum reduction in gain from said specificgain of said array means.

6. An electronic scanning antenna system as de' scribed in claim 1 inwhich said array means includes means for producing a diverging firstbeam of electromagnetic energy having a pre-determined non-planar phase,said array means being capable of producing a first beam ofelectromagnetic energy at a specific gain over a limited scan range.

7. An electronic scanning antenna system as described in claim 6 inwhich said lens means includes means for varying said phase gradient toproduce a second beam of electromagnetic energy having a plane wavefrontand a reduced range of scan with respect to said limited range of scanand an attendant increase in gain over said specific gain.

8. An electronic scanning antenna system as described in claim 6 inwhich said lens means includes a fixed phase gradient for transmitting adirective second beam of electromagnetic energy having a plane wavefrontand a reduced range of scan with respect to said limited range of scanand an increase in gain over said specific gain of said array means.

9. An electronic scanning antenna system as described in claim 1 inwhich said array means further includes means for providing a convergingfirst beam in a first direction and means for providing a divergingfirst beam in a second direction, and

said lens means includes means for varying said phase gradient forproducing, in response to said converging first beam, a second beam ofelectromagnetic energy having a plane wavefront directed in said firstdirection within a first prescribed range of scan with an attendantreduction in gain from said specific gain and means for varying saidphase graclient for producing, in response to said diverging first beam,a second beam of electromagnetic energy having a plane wavefrontdirected in said second direction within a prescribed range of scan withan attendant increase in gain over said specific gain thereby providingan antenna system having a minimum number of elements.

10. An electronic scanning antenna system as described in claim 1 inwhich said array means includes collector elements for receiving saidelectromagnetic energy provided by said source of electromagneticenergy,

electronically controlled phase shifter elements coupled to saidcollector elements and radiator elements coupled to said electronicallycontrolled phase shifter elements.

ll. An electronic scanning antenna system as described in claim 1 inwhich said lens means includes collector elements for receiving saidfirst beam of electromagnetic energy,

variable phase shifter elements coupled to said collector elements forimplementing said phase gradient, and radiator elements coupled to saidvariable phase shifter elements for transmitting said directive secondbeam of electromagnetic energy.

12. An electronic scanning antenna system as described in claim 1 inwhich said lens means includes a lens having a non-planar shape.

13. An electronic scanning antenna system as described in claim 12 inwhich said lens has a spherical configuration.

14. An electronic scanning antenna system as described in claim 12 inwhich said lens means includes a lens having a cylindricalconfiguration.

15. An electronic scanning antenna system as described in claim 1 inwhich said lens means is portable.

16. An electronic scanning antenna system as described in claim 1 inwhich said lens means includes a lens of dielectric material having avariable thickness and non-planar shape whereby the focal properties ofsaid lens are controlled in accordance with said variable thickness andnon-planar shape.

17. An electronic scanning antenna system as described in claim 16 inwhich said lens has a geometrical shape which conforms to the noseprofile of a high speed vehicle.

18. An electronic scanning antenna system as described in claim 16 inwhich said lens is fabricated of titanium dioxide.

19. An electronic scanning antenna system as described in claim 1 inwhich said lens means includes dipole collector elements for receivingsaid first beam of electromagnetic energy,

flexible cables of varying length coupled to said dipole collectorelements, and

dipole radiator elements coupled to said flexible ca bles fortransmitting said directive second beam of electromagnetic energy.

20. An electronic scanning antenna system as described in claim 1 inwhich said lens means includes open-ended collector elements forreceiving said first beam of electromagnetic energy,

dielectrically loaded circular waveguides coupled to said collectorelements for imparting different relative phase delays to said firstbeam, and open-ended radiator elements coupled to said circularwaveguides for transmitting said directive second beam having a planewavefront.

1. An electronic scanning antenna system comprising a source ofelectromagnetic energy, array means including elements, said array meansbeing coupled to said source of electromagnetic energy for producing afirst beam of electromagnetic energy having a non-planar phase andcontrollable focal properties, and lens means responsive to said firstbeam of electromagnetic energy having a non-planar phase andcontrollable focal properties which implement a phase gradient forproducing a directive second beam of electromagnetic energy having aplane wavefront, a variable range of scan and an attendant variablegain.
 2. An electronic scanning antenna system as described in claim 1in which said source of electromagnetic energy includes a radiating feedhorn.
 3. An electronic scanning antenna system as described in claim 1in which said array means coupled to said source of electromagneticenergy includes means for producing a converging first beam ofelectromagnetic energy having a pre-determined non-planar phase, saidarray means being capable of producing a first beam of electromagneticenergy at a specific gain over a limited range of scan.
 4. An electronicscanning antenna system as described in claim 3 in which said lens meansincludes means for varying said phase gradient whereby said second beamof electromagnetic energy has an increased range of scan over saidlimited range of scan with an attendant minimum reduction of gain fromsaid specific gain.
 5. An electronic scanning antenna system asdescribed in claim 3 in which said lens means has a fixed phase gradientin all directions for transmitting a directive second beam ofelectromagnetic energy having a plane wavefront and an increased rangeof scan over said limited range of scan with an attendant minimumreduction in gain from said specific gain of said array means.
 6. Anelectronic scanning antenna system as described in claim 1 in which saidarray means includes means for producing a diverging first beam ofelectromagnetic energy having a pre-determined non-planar phase, saidarray means being capable of producing a first beam of electromagneticenergy at a specific gain over a limited scan range.
 7. An electronicscanning antenna system as described in claim 6 in which said lens meansincludes means for varying said phase gradient to produce a second beamof electromagnetic energy having a plane wavefront and a reduced rangeof scan with respect to said limited range of scan and an attendantincrease in gain over said specific gain.
 8. An electronic scanningantenna system as described in claim 6 in which said lens means includesa fixed phase gradient for transmitting a directive second beam ofelectromagnetic energy having a plane wavefront and a reduced range ofscan with respect to said limited range of scan and an increase in gainover said specific gain of said array means.
 9. An electronic scanningantenna system as described in claim 1 in which said array means furtherincludes means for providing a convErging first beam in a firstdirection and means for providing a diverging first beam in a seconddirection, and said lens means includes means for varying said phasegradient for producing, in response to said converging first beam, asecond beam of electromagnetic energy having a plane wavefront directedin said first direction within a first prescribed range of scan with anattendant reduction in gain from said specific gain and means forvarying said phase gradient for producing, in response to said divergingfirst beam, a second beam of electromagnetic energy having a planewavefront directed in said second direction within a prescribed range ofscan with an attendant increase in gain over said specific gain therebyproviding an antenna system having a minimum number of elements.
 10. Anelectronic scanning antenna system as described in claim 1 in which saidarray means includes collector elements for receiving saidelectromagnetic energy provided by said source of electromagneticenergy, electronically controlled phase shifter elements coupled to saidcollector elements and radiator elements coupled to said electronicallycontrolled phase shifter elements.
 11. An electronic scanning antennasystem as described in claim 1 in which said lens means includescollector elements for receiving said first beam of electromagneticenergy, variable phase shifter elements coupled to said collectorelements for implementing said phase gradient, and radiator elementscoupled to said variable phase shifter elements for transmitting saiddirective second beam of electromagnetic energy.
 12. An electronicscanning antenna system as described in claim 1 in which said lens meansincludes a lens having a non-planar shape.
 13. An electronic scanningantenna system as described in claim 12 in which said lens has aspherical configuration.
 14. An electronic scanning antenna system asdescribed in claim 12 in which said lens means includes a lens having acylindrical configuration.
 15. An electronic scanning antenna system asdescribed in claim 1 in which said lens means is portable.
 16. Anelectronic scanning antenna system as described in claim 1 in which saidlens means includes a lens of dielectric material having a variablethickness and non-planar shape whereby the focal properties of said lensare controlled in accordance with said variable thickness and non-planarshape.
 17. An electronic scanning antenna system as described in claim16 in which said lens has a geometrical shape which conforms to the noseprofile of a high speed vehicle.
 18. An electronic scanning antennasystem as described in claim 16 in which said lens is fabricated oftitanium dioxide.
 19. An electronic scanning antenna system as describedin claim 1 in which said lens means includes dipole collector elementsfor receiving said first beam of electromagnetic energy, flexible cablesof varying length coupled to said dipole collector elements, and dipoleradiator elements coupled to said flexible cables for transmitting saiddirective second beam of electromagnetic energy.
 20. An electronicscanning antenna system as described in claim 1 in which said lens meansincludes open-ended collector elements for receiving said first beam ofelectromagnetic energy, dielectrically loaded circular waveguidescoupled to said collector elements for imparting different relativephase delays to said first beam, and open-ended radiator elementscoupled to said circular waveguides for transmitting said directivesecond beam having a plane wavefront.